Recent literature on the evolution and interrelationships of the Caryophyllidea based on molecular and morphological criteria is reviewed. Molecular analyses with SSU rDNA, LSU rDNA and ef-1 alpha reaffirms the basal or near basal position of these nonozoic cestodes. Major emphasis is on an evaluation of the scoring in morphological character matrices used in cladistic studies. Suggested changes to present scoring are: uterus is dorsal; scolex is afossate, fossate or difossate with little support for monofossate; ciliated coracidium is absent; vitellaria are circum-cortical and circum-medullary; testes are cortical and medullary; metacercoid stage is absent; and the spermatozoan lacks a crested body, flagellar rotation and proximodistal fusion. Of the 41 recognized genera of the Caryophyllidea, 59% have an afossate scolex and the remainders are fossate. The use of a new character, “nuclear vacuole” in the nucleus of mature vitellocytes, is suggested. To aid in identifying cestode body types in an evolutionary context, they are designated as monopleuroid, polypleuroid and strobila. Tabulated differences between the monozoic Caryophyllidea and polyzoic eucestodes suggest that the two groups may warrant separate taxonomic status. The question of whether or not the monozoic state is primary or secondarily derived is not resolved. Using the life cycle characterstics of the Pseudophyllidea and of Archigetes as models, it is hypothesized that progenesis may have played a major role in the evolution of the Caryophyllidea. If the role of progenesis can be substantiated through total evidence incorporating cytohistological data, then the monozoic condition becomes coincidental and the hypothesis is not supported that the Caryophyllidea are ancestral and preceded polyzoic eucestodes.
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